Zeolite-based catalysts, such as MCM-22, are effective catalysts for hydrocarbon conversion reactions, such as the liquid phase alkylation of benzene with olefins to yield monoalkylated products with high selectivity. As in all catalytic processes, the catalyst deactivates with time on stream and needs to be regenerated to recover activity. Typically, zeolite catalysts are regenerated ex situ by flowing air to burn off coke and remove other deactivating species. However, in addition to loss in production time for catalyst removal, shipment, off-site regeneration, and replacement, conventional air regeneration of these catalysts results in a drop in the monoalkylation selectivity.
For example, the Mobil/Raytheon process for producing cumene involves the liquid phase alkylation of benzene with propylene, followed by transalkylation of di- and tri- isopropyl benzene with benzene. MCM-22 has been used successfully as the alkylation and transalkylation catalysts in this process and is particularly attractive because of its high selectivity towards monoalkylated products. However, the regeneration of used cumene catalysts, such as MCM-22 and the like, at the end of their cycles has been shown to result in an increase in the amounts of undesirable polypropylbenzenes and other heavy byproducts formed during subsequent operations. This results in a significantly increased duty on the transalkylator and a consequent drop in overall yield and product purity. It is highly desirable therefore to adopt a regeneration protocol which minimizes this change in the selectivity to undesirable byproducts.
There is a need in the art to provide a process for regenerating zeolite-based, aromatic alkylation catalysts without the drawbacks discussed above.
According to the invention, it has now been found that stripping in a light hydrocarbon gas stream like propane at relatively mild conditions effectively rejuvenates spent aromatic alkylation catalyst without any loss in the monoalkylation selectivity. The novel procedure of the present disclosure provides an efficient and convenient way for in situ regeneration of spent aromatic alkylation catalysts, significantly enhancing their re-use value.